With regard to whether Doug should be measuring Patient Leakage from his
bedframe:-
I believe the bedframe is an Applied Part under the definition of the
general standard 60601-1; ("AP = a part of the equipment which in normal use
.....can be brought into contact with the patient ....") ie: contact isn't
necessary for the device to perform its function, but contact could happen
during use - which is the case for hospital bedframes.
Under the particular standard for electric beds IEC-60601-2-38, "AP = all
parts of the bed which can intentionally or unintentionally come into
contact with the patient..."). There is a diagram in the edition we have
(1996) showing which areas of the bedframe are thus included.
My interpretation is then that the bedframe should be considered an AP and
so, as Doug says, it should be tested for Patient Leakage. If it were not an
AP it would have to be tested for Enclosure Leakage anyhow - in both cases
the limits for ac leakage are 0.1mA Normal Condition and 0.5mA Single Fault
Condition (though for Patient Leakage there are dc limits too).
If you are measuring 0.1mA leakage through the specified measuring device,
which simulates a patient impedance, then how low the voltage is on the
earthed frame is kind of immaterial - it is the current not the voltage that
the patient will feel. (The leakage likely has high impedance origins which
are better modelled as a current source than a voltage source).
Ged Dean
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